1. Field of the Invention
The present invention relates to a method for coating a particle core material with a precise amount of a liquid coating, and to a method of encapsulating a core particle via interfacial polymerization.
2. Discussion of Related Art
Various methods are known for applying a coating to particulate materials.
However, an area of continuing need in this technology is the development of a method that permits precise control over the amount of coating material applied to the particles.
This need is particularly evident in interfacial polymerization applications for deriving a polymeric shell around a particle core. Interfacial polymerization has been used in the field of making toners, for example encapsulated colored heat fusible toner compositions. See, for example, U.S. Pat. Nos. 5,035,970, 5,139,915, 5,077,167 and 5,082,757, incorporated herein by reference in their entire
U.S. Pat. No. 4,738,898 is directed to microencapsulation by interfacial polyaddition of, for example, an aliphatic diisocyanate and an isocyanurate triamer, and wherein the aforementioned components can be interfacially reacted with a polyamine; note the disclosure in column 3, beginning at line 46, wherein it is indicated that it is envisioned, for example, to encapsulate plant protection agents such as herbicides, fingicides, or insecticides, which makes them less hazardous to handle, and it is also intended to encapsulate the pharmaceutical products, food products, flavors, perfumes, colorants, paints, or catalysts, reference the disclosure in column 3, beginning at line 46.
U.S. Pat. No. 4,766,051 is directed to colored encapsulated toner compositions comprised of a core containing a polymer in which is dispersed pigment particles selected from the group consisting of cyan, magenta, red, yellow pigments, and mixtures thereof, and magnetites encapsulated within a polymeric shell formulated by an interfacial polymerization. For the interfacial polymerization, the organic phase can be dispersed by a polytron in an aqueous phase containing polyvinyl alcohol to obtain toner particles.
U.S. Pat. No. 4,727,101 illustrates a free radical polymerization of a toner shell at elevated temperatures and more specifically is directed to the preparation of encapsulated toner compositions, which comprises mixing in the absence of a solvent a core monomer, initiator, pigment particles, a first shell monomer, stabilizer, and water, and thereafter adding a second shell monomer to enable interfacial polymerization interaction, and subsequently affecting the free radical polymerization of the core monomer.
U.S. Pat. No. 4,702,988 illustrates a process for the preparation of encapsulated toner. A monomer composition and a colorant are dispersed in a liquid dispersion medium in the presence of a solid fine powdery dispersion stabilizer. The liquid is pressurized and then ejected into a low pressure section to form particles of monomer composition. These particles are then subjected to suspension polymerization to produce toner particles.
U.S. Pat. No. 4,727,011 discloses a process for preparing encapsulated toner compositions, which comprises mixing, in the absence of a solvent, a core monomer, an initiator, pigment particles, a first shell monomer, stabilizer, and water; thereafter adding a second shell monomer, thereby enabling an interfacial polymerization reaction between the first and second shell monomers; and subsequently effecting a free radical polymerization of the core monomer.
U.S. Pat. No. 4,851,318 discloses an improved process for preparing encapsulated toner compositions which comprises mixing core monomers, an initiator, pigment particles, and oil soluble shell monomers, homogenizing the mixture into an aqueous surfactant solution to result in an oil-in-water suspension enabling an interfacial polymerization reaction between the oil soluble and the water soluble shell monomers, subsequently adding a low molecular weight polyethylene oxide surfactant protective colloid, and thereafter effecting free radical polymerization of the core monomers by heating.
Another recent application of interfacial polymerization is described in copending U.S. application Ser, No. 09/722,334, filed Nov. 28, 2000, where rotatable gyricon spheres are encapsulated along with a dielectric fluid within a polymeric shell formed by interfacial condensation polymerization. This copending application is incorporated herein by reference in its entirety.
Methods of providing coatings to particles for forming membranes or encapsulating shells around the particles still require improvement with respect to providing an accurate and precise amount of coating to the particles. Further, it would also be desirable to develop a method not requiring immersion of the coating into an aqueous composition for polymerization as such requires recovery and washing steps to also be used.
It is therefore an object of the present invention to develop a method for dosing particulate cores with an accurate and precise amount of coating.
It is a still further object of the present invention to develop a method of coating particulate cores with a coating that eliminates the need for dispersion within an aqueous composition.
It is a still further object of the present invention to develop a simplified method of forming a shell around a particulate core via interfacial condensation polymerization.
These and other objects of the present invention are achieved herein by a method of coating a liquid or solid particulate core in which the method comprises dropping or suspending the particulate core in an atmosphere and then applying a liquid coating while the particulate core is dropped or suspended, the applying of the liquid coating comprising either (a) spraying the liquid coating onto the particulate core with an ink jet or (b) moving the particulate core through a fog of the liquid coating.
These and other objects of the invention are also achieved by a method for encapsulating a liquid or solid particulate core within a polymeric shell in which the method comprises dropping or suspending the particulate core in an atmosphere, then applying a first coating composition containing a first reactant to the particulate core while the particulate core is being dropped or suspended, the applying of the first coating composition comprising (a) spraying the first coating composition onto the particulate core with an ink jet or (b) moving the particulate core through a fog of the first coating composition, and subsequently exposing the particulate core coated with the first coating composition to a second composition containing a second reactant which reacts with the first reactant, which second composition is immiscible with the first coating composition, whereby the polymeric shell is formed by interfacial polymerization.
The invention enables the formation of membranes or polymer shells around a variety of particulate core materials, and is most suitable for coating a core surrounded by a fluid, all of which is encapsulated within a polymer skin or shell (as in encapsulated gyricon spheres), using precise amounts of coating materials, thereby reducing waste and improving efficiencies of the process.